The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-381884 filed on Dec. 14, 2001 and Japanese Patent Application No.2002-248548 filed on Aug. 28, 2002, which are incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a driving apparatus used with an image formation apparatus, such as a copier or a printer, and in particular to improvements in a driving apparatus for transmitting a driving force from a drive source to a driven body via a multiple-stage gear train and an image formation apparatus using the driving apparatus.
2. Description of the Related Art
Generally, as a technique of driving a driven body such as a photoconductor drum or an intermediate transfer body in an image formation apparatus such as a copier or a printer, a driving apparatus for transmitting a driving force from a drive source such as a motor to a driven body with a multiple-stage gear train (a gear train comprising a plurality of gears meshing with each other successively) is used (for example, refer to JP-A-61-156158).
At this time, the vibration component caused by the gears meshing with each other, a one-revolution component caused by eccentricity of a rotor of the motor, and the like enter the frequencies in the functional area of a human being and thus it is necessary to attenuate the components, etc., for providing stable rotation.
Hitherto, as a remedy, it has been generally known to attach a flywheel onto a driven body shaft of a photoconductor drum, etc., for increasing the inertia amount.
An art of attaching a flywheel of a small inertia body to a separate shaft from a driven body shaft of a photoconductor drum, etc., and increasing the speed of the flywheel, thereby giving a large inertia effect to the driven body is also known (for example, refer to Japanese Patent No. 3013779).
However, in this kind of flywheel technique, the number of parts is increased and the apparatus itself is upsized because of use of at least the flywheel as an inertia body. Thus, for example, to apply a driving apparatus of a multiple-stage gear train to a tandem image formation apparatus, etc., it is extremely difficult to apply the flywheel technique from the viewpoints of miniaturizing and making cheaper the image formation apparatus.
Hitherto, as a technique of decreasing speed fluctuation caused by a gear eccentricity component, a related art is proposed wherein the gears of a gear train are formed as gears of the same shape, for example, the same molded articles or integrally simultaneously worked molded articles and at the assembling time of the correspondence positions of the gears, the gears are selectively placed at the phase positions responsive to the speed fluctuation phases of gear shafts (for example, refer to JP-A-61-156158).
From V=r xcfx89 (where V: Speed, r: Gear radius, and xcfx89: Angular speed), gears are rotated so that the radiuses of the gears are made the same at the mesh points of the driving apparatus and driven gears, whereby the angular speeds of the driving apparatus and driven gears are made the same for decreasing the eccentricity component of each gear.
However, this type may cope with speed fluctuation caused by the eccentricity component of each gear, but still cannot cope with speed fluctuation caused by the mesh component of each gear.
A technique is disclosed wherein, for example, in a four-cycle intermediate transfer type image formation apparatus, (1) a configuration in which the rotation period of a photoconductor drum drive gear is roughly matched with the rotation period from light exposure to primary transfer and (2) a configuration in which the rotation period of an intermediate transfer body drive gear is roughly matched with the rotation period from primary transfer to secondary transfer are adopted, thereby preventing expansion or contraction of an image caused by the difference between the peripheral speed at an image write position onto a photoconductor drum and that at a transfer position and further preventing expansion or contraction of an image caused by the difference between the speed at the transfer time from the photoconductor drum and that at the transfer time to a record material (for example, refer to JP-A-9-43932).
In this technique, it may be possible to roughly cancel fluctuation (color shift) of the one-revolution period of the photoconductor drum and an intermediate transfer body, caused by the eccentricity of the gears for driving the photoconductor drum and the intermediate transfer body, but an image defect (banding) caused by expansion or contraction of an image caused by the speed fluctuation of gear mesh frequency is not remedied at all; this is a technical problem.
It is therefore an object of the invention to provide a driving apparatus for making it possible to effectively prevent speed fluctuation caused by the mesh components of a multiple-stage gear train without upsizing the driving apparatus itself and an image accumulation apparatus using the driving apparatus.
The inventor et al. analyzed the mesh state of a gear pair of a multiple-stage gear train model and recognized that the mesh state of gear teeth of a G1 and G2 gear pair changed from moment to moment and the number of mesh points h became two or one and that speed fluctuation was caused by the mesh components of the multiple-stage gear train based on such a behavior, as shown in FIGS. 37(a) to 37(c) and FIGS. 38(a) and (b).
When the mesh state of the gear teeth at each mesh point of the G1 and G2 gear pair was changed in the multiple-stage gear train model, for example, with a crest crest mesh transmission technique (transmission technique in which when the gear tooth at the input side mesh point of the gear G1 is a crest position, the gear tooth at the output side mesh point of the gear G1, namely, at the mesh point with the gear G2 is a crest position), the results of the speed fluctuations of the gears G1 and G2 and the difference between the speed fluctuations were obtained as shown in FIG. 39.
On the other hand, with a crest trough mesh transmission technique (transmission technique in which when the gear tooth at the input side mesh point of the gear G1 is a crest position, the gear tooth at the output side mesh point of the gear G1, namely, at the mesh point with the gear G2 is a trough position), the results of the speed fluctuations of the gears G1 and G2 and the difference between the speed fluctuations were obtained as shown in FIG. 40.
When the speed fluctuation difference between the gears G1 and G2 in the crest crest mesh transmission technique was compared with that in the crest trough mesh transmission technique, the result shown in FIG. 41 was obtained and a clear difference was observed between the speed fluctuation difference waveforms.
Then, the inventor et al. obtained the knowledge that the gear speed fluctuation might be able to be controlled by changing the mesh state at each mesh point of the multiple-stage gear train, and have thought out the invention.
That is, as shown in FIG. 1, according to the invention, there is provided a driving apparatus for transmitting a driving force from a drive source 1 to a driven body (not shown) via a multiple-stage gear train 2 (consisting of, for example, gears 2a to 2c), characterized in that in the multiple-stage gear train 2, the speed fluctuation phase of a mesh frequency occurring at each mesh point of the gear train consisting of the gears 2a to 2c to a target gear 2c is set in the range in which the speed fluctuation amplitude of the target gear 2c positioned downstream at the third stage or later is equal to or less than the speed fluctuation amplitude of the immediately preceding mesh gear 2b positioned upstream.
In such technical means, the multiple-stage gear train 2 refers to the form of a train of a large number of gears meshing with each other. Each of the gears 2a to 2c making up the multiple-stage gear train 2 may be a one-step gear or a multiple-step gear.
Preferably, if at least one of the gears of the multiple-stage gear train 2, for example, the gear 2a is implemented as a multiple-step gear (in the example, two-step gear), the number of the gear stages of the gear train can be decreased because of use of the multiple-step gear.
In FIG. 1, the multiple-stage gear train 2 is made up of the three gears 2a to 2c meshing with a drive shaft gear 1a of the drive source 1, but the invention is not limited to it. Various forms such as a multiple-stage gear train made up of a different number of gear stages and a multiple-stage gear train with a gear stage branching at an intermediate point.
The number of the driven bodies need not be one and may be two or more.
Further, the target gear 2c is not limited to the last stage gear and an intermediate stage gear is also contained. Usually, the driven body is directly joined to the target gear 2c, but a target gear to which the driven body is not directly joined is also contained.
Further, the target gear 2c positioned downstream at the third stage or later assumes the case where there are two or more mesh points to the target gear 2c. 
The number of the target gears 2c may be one or may be two or more.
The form in which the number of the target gears 2c is two or more may be the form in which the numbers of gear stages of the multiple-stage gear train 2 from the drive source 1 are different or the same.
If the speed fluctuation amplitude of the target gear 2c is in the range equal to or less than the speed fluctuation amplitude of the immediately preceding mesh gear 2b positioned upstream, the speed fluctuation phase of the mesh frequency at each of mesh points A and B (in FIG. 1, the number of mesh points is two, but is not limited to two, of course) may be adjusted appropriately.
Particularly, most preferably, the range equal to or less than the speed fluctuation amplitude of the immediately preceding mesh gear 2b is set so that the speed fluctuation amplitude of the target gear 2c reaches the minimum.
As a specific setting method of the speed fluctuation phase of the mesh frequency occurring at each of the mesh points A and B of the gear train of the gears 2a to 2c to the target gear 2c, the speed fluctuation phase of the mesh frequency may be set in response to the one-pitch angle of each of the gears 2a to 2c and the position between the mesh points of the gear train.
In the form wherein all or some of the gears 2a to 2c of the multiple-stage gear train including the target gear 2c are helical gears, the speed fluctuation phase of the mesh frequency occurring at each of the mesh points A and B of the gears 2a to 2c of the multiple-stage gear train to the target gear 2c may be set based on the axial mesh width of the helical gear at the helical gear mesh point.
This is intended for setting the gear tooth phase paying attention to the form of the helical gear (the gear tooth phase changes with the axial mesh width).
Particularly, preferably, if the face-width of an intermediate helical gear at an intermediate position in the multiple-stage gear train 2 is set smaller than the face-width of each of helical gears positioned above and below the intermediate helical gear and the intermediate helical gear is meshed with the up and down helical gears in all area of the face-width of the intermediate helical gear, the situation in which the speed fluctuation phase of the mesh frequency varies with the variation in the axial position of the helical gear is circumvented.
If a helical gear positioned at an end part of the multiple-stage gear train is formed as a phase adjustment gear movable in an axial direction, it is made possible to appropriately adjust the speed fluctuation phase of the mesh frequency occurring at each of the mesh points A and B, and it is made possible to finely adjust the speed fluctuation phase.
Further, in the form wherein all or some of the gears 2a to 2c of the multiple-stage gear train including the target gear 2c are helical gears, preferably a position regulation member for regulating an axial position of a helical gear is provided.
Because of the configuration of the helical gear, thrust easily occurs and if looseness is contained in the axial direction of the helical gear, there is a possibility that the speed fluctuation phase of the mesh frequency may change, causing speed fluctuation of the target gear 2c to occur.
However, according to the form, the position of the helical gear is regulated by the position regulation member, so that fluctuation of the speed fluctuation phase of the mesh frequency is suppressed.
A position regulation member shaped like a block, a bush, etc., may be selected appropriately if it regulates at least the axial position of the helical gear; it may regulate a position other than the axial position (for example, a direction orthogonal to the axial direction).
Further, the thrust of the helical gear itself may be used to provide the press force against the position regulation member of the helical gear in addition to providing the press force by a separate member.
In the invention, in the multiple-stage gear train 2, the target gear 2c may be driven at the same speed or with deceleration relative to the upstream mesh gear 2b or the target gear 2c may be driven at increased speed relative to the upstream mesh gear 2b. The adjustment method of the speed fluctuation phase of the mesh frequency varies depending on which mode is adopted.
For example, as a measure not to amplify the speed fluctuation amplitude of the target gear 2c in the same speed or deceleration mode, in the form wherein the driving apparatus comprises an at least two-stage gear train of gears 2a and 2b upstream from the target gear 2c, of three-stage gear train consisting of the target gear 2c and the upstream two-stage gear train of the gears 2a and 2b, the phases of gear teeth at an output side mesh point B of the intermediate gear 2b and an input side mesh point A of the intermediate gear 2b may be shifted to roughly opposite phases.
However, the phase shift amount may be in a range in which the speed fluctuation amplitude of the target gear 2c is not amplified, and thus the phases need not precisely be opposite phases and a predetermined allowed width exists for the opposite phase; in this point, roughly opposite phases are adopted.
In the form wherein the driving apparatus comprises an at least two- or-more-stage gear train of gears 2a, 2b . . . upstream from the target gear 2c, the phases of gear teeth at mesh points A, B . . . of the gear train consisting of the target gear 2c and the upstream two-or-more-stage gear train of gears 2a, 2b . . . contiguous with the target gear 2c may be shifted in response to the shift angle provided by dividing 360 degrees by the number of mesh points.
This means that if the gear train is an n-stage gear train, the number of mesh points is nxe2x88x921 and thus the phases are shifted at the shift angle of 360xc2x0/(nxe2x88x921).
In this case, the gear tooth phase difference may be canceled at the mesh point of the target gear 2c. 
As a measure not to amplify the speed fluctuation amplitude of the target gear 2c in a speed increasing mode, in the form wherein the driving apparatus comprises an at least two-stage gear train of gears 2a and 2b upstream from the target gear 2c, of three-stage gear train consisting of the target gear 2c and the upstream two-stage gear train of the gears 2a and 2b, the phases of gear teeth at an output side mesh point B of the intermediate gear 2b and an input side mesh point A of the intermediate gear 2b may be set roughly to the same phases.
However, the phase shift amount maybe in a range in which the speed fluctuation amplitude of the target gear 2c is not amplified, and thus the phases need not precisely be the same phases and a predetermined allowed width exists for the same phase; in this point, roughly same phases are adopted.
Thus, the speed increasing mode and the same speed or deceleration mode differ in gear tooth behavior at the mesh point (it is estimated that such a phenomenon depends on the difference between the slip ratios at the mesh start and end of gear teeth) and thus the adjustment method of the speed fluctuation phase differs.
In the mesh frequency of the multiple-stage gear train, harmonic components of double wave, triple wave, etc., may occur in addition to the fundamental component.
Therefore, xe2x80x9csetting the speed fluctuation phase of the mesh frequencyxe2x80x9d includes not only setting centering around the fundamental component, but also setting centering around the harmonic component.
For example, if the harmonic component of a mesh frequency mainly occurs in a driving apparatus including a multiple-stage gear train, the speed fluctuation phase of the mesh frequency may be set so as to cancel out the speed fluctuation of the harmonic component.
As the means for canceling out the speed fluctuation phase of the harmonic component, for example, if the mesh frequency is changed because of double gear, etc., at an intermediate point of the multiple-stage gear train, setting the changed mesh frequency to an integral multiple of the former mesh frequency or the like can be named.
The invention applies not only to the driving apparatus, but also to an image formation apparatus using the driving apparatus.
In this case, the driving apparatus may be used as a driving apparatus of a driven body such as an image support.
As a specific application example to the image formation apparatus, taking an intermediate transfer type as an example, the image formation apparatus can comprise an image formation support for forming and supporting an image and an intermediate transfer body for temporarily supporting the image on the image formation support, transporting the image, and transferring the image onto a record material and using a driving apparatus for transmitting a driving force from one drive source to the intermediate transfer body and the image formation support in order.